This invention relates to electronic test systems, and more particularly to robotic testers for memory modules including SIMMs and DIMMs.
Personal computers (PCs) commonly use DRAM memory chips mounted on small, removable memory modules. The original single-inline memory modules (SIMMs) have been replaced with dual-inline memory modules (DIMMs), and 184-pin RIMMs (Rambus inline memory modules) and 184-pin DDR (double data rate) DIMMs.
The memory-module industry is very cost sensitive. Testing costs are significant, especially for higher-density modules. Specialized, high-speed electronic test equipment is expensive, and the greater number of memory cells on high-speed memory modules increases the time spent on the tester, increasing costs.
Handlers for integrated circuits (ICs) have been used for many years in the semiconductor industry. Handlers accept a stack of IC chips that are fed, one at a time, to the tester. The tested IC is then sorted into a xe2x80x9cbinxe2x80x9d for IC chips that have passed or failed the test.
More recently, handlers have been made for memory modules. U.S. Pat. No. 5,704,489 by Smith, describes in detail a xe2x80x9cSIMM/DIMM Board Handlerxe2x80x9d such as those in use today. FIG. 1 shows a SIMM handler connected to a high-speed electronic tester. Memory modules 18 to be tested are loaded into the top of handler 10 in the input stack. Memory modules 18 drop down, one-by-one, into testing area. Module-under test MUT 20 is next to be tested. Arm 26 pushes MUT 20 laterally until it makes contact with contactor pins 16 that clamp down on xe2x80x9cleadlessxe2x80x9d connector pads formed on the substrate of MUT 20.
Contactor pins 16 are also connected to test head 14, which makes connection to tester 12. Tester 12 executes parametric and functional test programs that determine when MUT 20 falls within specified A.C. and D.C. parameters, and whether all memory bit locations can have both a zero and a one written and read back.
Tester 12 can cost from ten-thousand to millions of dollars. Cost can be reduced if a less-expensive tester replaces tester 12. Since most memory modules are intended for installation on PCs, some manufacturers test memory modules simply by plugging them into SIMM or DIMM sockets on PC motherboards. A test program is then executed on the PC, testing the inserted module. Since PCs cost only about a thousand dollars, tester 12 and handler 10 of FIG. 1 are replaced by a low-cost PC. Equipment costs are thus reduced by a factor of a hundred.
FIG. 2 shows a PC motherboard being used to manually test memory modules. Substrate 30 is a motherboard. Components 42, 44, mounted on the top side of substrate 30, include ICs such as a microprocessor, logic chips, buffers, and peripheral controllers. Sockets for expansion cards 46 are also mounted onto the top or component side of substrate 30.
Memory modules 36 are SIMM or DIMM modules that fit into SIMM/DIMM sockets 38. SIMM/DIMM sockets 38 (hereinafter SIMM sockets 38) have metal pins that fit through holes in substrate 30. These pins are soldered to solder-side 34 of substrate 30 to rigidly attach SIMM sockets to the PC motherboard. Both electrical connection and mechanical support are provided by SIMM sockets 38.
While using PC motherboards for testing memory modules greatly reduces equipment costs, labor costs are increased. Memory modules must be inserted and removed manually. Manual insertion and removal of memory modules is slow and labor-intensive.
The parent application teaches that the component side of the PC motherboard is too crowded for attaching a SIMM/DIMM handler. However, the inventors have realized that the back or solder-side of the PC motherboard is less crowded and provides unobstructed access. The PC motherboard is modified to provide reverse attachment of the handler to the solder-side of the PC motherboard using a handler adapter board. The SIMM socket on the component side of the PC motherboard is removed, and the handler adapter board is plugged from the backside into the holes on the PC motherboard for the SIMM socket.
Handler Mounted Close to PC Motherboardxe2x80x94FIG. 3
FIG. 3 shows that the SIMM/DIMM handler is mounted close to the backside of the PC motherboard using the handler adaptor board. Handler 10 is not drawn to scale since it is several times larger than a PC motherboard. However, FIG. 3 does highlight how handler 10 can fit close to the removed SIMM socket. Such close mounting reduces loading and facilitates high-speed testing.
Contactor pins 16 within handler 10 clamp down onto leadless pads on the edge of module-under-test MUT 20 when arm 26 pushes MUT 20 into place for testing. Contactor pins 16 are electrically connected to connectors on the backside of handler 10. These connectors are edge-type connectors that normally connect with high-speed testers. Typically two connectors are provided. These male-type connectors fit into female-type connectors 54 mounted on handler adaptor board 50. Handler adaptor board 50 contains metal wiring traces formed therein that route signals from connectors 54 to adaptor pins 52 that protrude out the other side of handler adaptor board 50.
Adaptor pins 52 can be plugged into female pins 55 that are soldered onto solder-side 34 of the PC motherboard. Female pins 55 have extensions that fit into the through-holes exposed by removal of the SIMM socket, but also have cup-like receptacles for receiving adaptor pins 52. Using female pins 55 allows handler adaptor board 50 to be easily removed from substrate 30.
Once MUT 20 has been tested by a test program running on the PC motherboard, MUT 20 is sorted and drops down into either good bin 22 or bad bin 24. Sorting is in response to a pass/fail signal from the test program running on the PC motherboard.
Handler adaptor board 50 provides electrical connection from the module-under-test (MUT) in handler 10 to the removed SIMM socket on the PC motherboard. Handler adaptor board 50 provides a slight spacing or offset from the solder-side 34 surface of substrate 30, allowing handler 10 to be plugged directly into connectors 54 on handler adaptor board 50. Since the offset of adaptor board 50 is slight, the length of electrical connections to the handler is short, minimizing added loading on the PC""s memory bus. The relatively flat surface of solder-side 34 allows close mounting of the SIMM/DIMM handler to the PC motherboard.
While the invention described in the parent application has been quite effective, further improvements are desired. Handlers are large, bulky machines that have a tendency to jam up, requiring that a technician un-jam the modules in the handler. While such memory-module handlers are useful, the inventors desire to replace the handler with robotic technology. Robotic arms do not suffer from the jamming problem of modules in a gravity-fed handler.
Newer modules contain xe2x80x9ctinyxe2x80x9d discrete components (resistors, capacitors) used for filtering signals and clocks. These components are sometimes taller than the memory chips on the module. The discrete components can become dislodged as the modules trickle down the input stack of a gravity-fed handler. Depending on how the components are placed on the module, one side of the module may be taller than the other side, creating an xe2x80x9cimbalancexe2x80x9d on the modules in the stack. This is major cause for jamming and dislocation of small components.
One memory-module handler is needed for each motherboard. These handlers are still somewhat expensive. A parallel test system with many motherboards each with an adaptor board is desired to increase the throughput of the testing system. Automated visual inspection of passed memory modules is also desired. It is desirable to integrate automated visual inspection with the test system, to reduce manual visual checks of the modules. Costs can then be further reduced.
A parallel test system for testing memory modules has a plurality of motherboards. The motherboards are main boards for computers that use memory modules as a memory.
The motherboards have a component side and a solder side. The component side has integrated circuits mounted thereon and expansion sockets for expansion boards.
Test adaptor boards are mounted to the solder side of the motherboards. The test adaptor boards have test sockets that receive memory modules for testing by the motherboards. Each test adaptor board electrically connects a memory module inserted into the test socket to a motherboard attached to the test adaptor board. The motherboard uses the memory module inserted into the test socket as a portion of the memory of the motherboard.
A main system interface is coupled to the plurality of motherboards. It commands the motherboards to test memory modules inserted into the test sockets and receives test results from the motherboards.
A robotic arm is responsive to commands from the main system interface. It inserts memory modules into the test sockets. Thus the robotic arm inserts memory modules into the test sockets on the test adaptor boards mounted on the solder side of the motherboards.
In further aspects of the invention each motherboard is mounted with the solder side facing upwardly. The expansion boards are below the motherboard. The robotic arm moves above the plurality of motherboards, reaching the test sockets on the test adaptor boards mounted above the solder side of the motherboards. Thus movement of the robotic arm is not obstructed by the expansion boards and integrated circuits mounted on the component side of the motherboards.
In further aspects an input tray holds untested memory modules. The robotic arm picks a memory module from the input tray and inserts the memory module in one of the test sockets for testing by one of the motherboards. An output tray holds tested memory modules. The main system interface commands the robotic arm to pull a memory module from a test socket attached to a motherboard that sent a passing test result to the main system interface and place the memory module on the output tray. Thus the robotic arm moves memory modules from the input tray to motherboards for testing, and moves passing memory modules from the motherboards to the output tray.
In still further aspects of the invention a camera is positioned to capture an image of a memory module held by the robotic arm. An image processor is coupled to receive the image from the camera. It compares the image to a reference image and determining when the image differs sufficiently from the reference image to fail a visual inspection. A VI tray holds memory modules that fail the visual inspection. The robotic arm moves the memory module to the VI tray when the image processor indicates that the memory module failed the visual inspection. Thus visual inspection is performed by the parallel test system. The visual inspection is performed in-transit.
In other aspects the motherboards are personal computer PC main boards and the expansion boards include a network interface expansion board and the plurality of motherboards includes at least 4 motherboards.